ramips: fix usb phy compatible string (should fix FS#1489)

In the new USB phy driver, it checks the compatible string before
attempting to iomap its mem resource and do the extra PHY init

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/ramips/dts/mt7628an.dtsi

@@ -373,7 +373,7 @@
 	};
 
 	usbphy: usbphy@10120000 {
-		compatible = "ralink,mt7628an-usbphy", "mediatek,mt7620-usbphy";
+		compatible = "mediatek,mt7628-usbphy", "mediatek,mt7620-usbphy";
 		reg = <0x10120000 0x1000>;
 		#phy-cells = <0>;